Patients with allergic diseases invariably have elevated IgE levels. The acquisition of specific immune sensitivity to allergens in these same individuals is linked to their cumulative environmental allergen exposure. These associations suggest that IgE may promote allergic sensitization. Recent data from this laboratory have established such a function for IgE antibodies in contact sensitivity responses, where they enhance immune sensitization to epicutaneously-applied chemical haptens using a mechanism that requires their interaction with mast cells via FcEepsilonRI. Preliminary studies have shown that responses to contact sensitizers are markedly impaired in IgE-/- and mast cell-deficient (W/W') mice as well as animals lacking FcepsilonRI. IgE antibodies support the production of cytokines by mast cells in irritant-exposed skin in an antigen-independent manner consistent with monomeric IgE signaling. The skin of both mast cell- and IgE-deficient animals has abnormally low levels of TNF, a mast cell cytokine previously shown to be critical in contact sensitivity. Intradermal injection of TNF completely restores the contact sensitivity responses of IgE-/- and W/W' mice. Pulmonary responses to contact sensitizers are also IgE-dependent. These findings give rise to the hypothesis that IgE primes dermal mast cells for irritant-induced production of TNF and IL-6 and that these mast cell-derived cytokines activate tissue dendritic cells to drive effective immune sensitization. This hypothesis will be examined with the following aims: I. The contact sensitivity system will be used to establish the effects of mast cells and of mast cell-derived cytokines TNF and IL-6 on dermal dendritic cells and Langerhans cells. ll. The "priming" function of IgE antibodies for mast cell responses to chemical irritants and secretagogues and the mechanism of monomeric IgE signaling will be characterized in cultured mast cells and in vivo. III. A murine model of occupational asthma will be used to examine the roles of IgE antibodies, mast cells, IL-6 and TNF in the induction of airway inflammation following inhalation of contact sensitizers.